In the computer age of mass information processing, a major factor impeding computer applications are the weaknesses of the transducers available to translate the physical properties of objects into electrical signals with minimum disturbance. Transducers are needed that are fast, accurate, simple, reliable, inexpensive, and nondisruptive. Of the myriad techniques that can be used, resonant circuit sensors provide the distinct advantages of eliminating the need for physical contact with the measured objects, of having the potential for high speed, and of being able to simultaneously measure more than one property. Such sensors have been plagued in the past with complexity, instabilities, limited sensitivites, and high cost.
Many resonant circuit sensors are capable of only a single measurement capability, even though their output is sensitive to a variety of properties of often measured objects. This produces drift and stability problems and it becomes confusing as to which parameters are changing. Also such sensors frequently require rather complex, swept frequency, energy sources.
Resonant detectors of multiple parameters have been of two types--noninteractive and interactive. The noninteractive ones have no interactions between the measured substances and the oscillating wave fields of the resonators. Physical contact with the object is then required and a major advantage of resonant techniques is lost. Existing interactive techniques require precise, swept frequency oscillators for a detailed determination of the resonant sensor's response at frequencies on and off resonance in a manner that defines the quality factor or Q of the sensor. This, in turn, can be translated into two separate properties of the measured substances after complex calculations and calibrations for a limited range of measured properties. Accurate and repeatable measurements require sophisticated and experienced operators and elaborate equipment.
The present invention provides a high speed, noncontacting transducer to simultaneously convert physical properties of objects into electrical signals with high accuracy, good stability, relative simplicity, and low cost. It does not require the off resonance excitations needed for swept frequency Q measurements. It should provide increased capabilities for applications as diverse as frozen food processing, sterile manufacture of medical products, and transportation safety aids.